Can't launch Win 7 image from Windows 10 ("T-x is not available")

I'm running Windows 10 enterprise 64-bit on a i7-5600U processor and try to launch a Windows 7 image in Virtualbox. I have chosen a 32 bit version of W7, as there was no option to select a 64 bit Windows when I launched Virtualbox.

However, after setting RAM and HDD size, I get the following error message when trying to start the VM:

Failed to open a a session for the virtual machine **Win7-32**

which expands to

T-x is not available (VERR_VMX_NO_VMX).


Result Code: 
E_FAIL (0x80004005)
Component: 
ConsoleWrap
Interface: 
IConsole {872da645-4a9b-1727-bee2-5585105b9eed}

I've tried what suggestions I've come across, namely making sure Virtualization is enabled in UEFI and shutting down my active Hyper-v service.